N,N′-Bis(4-bromo-2-fluoro­benzyl­idene)ethane-1,2-diamine

Abstract

The mol­ecule of the title Schiff base compound, C₁₆H₁₂Br₂F₂N₂, lies across a crystallographic inversion centre and adopts an E configuration with respect to the azomethine C=N bonds. The imino groups are coplanar with the aromatic rings. Within the mol­ecule, the planar units are parallel, but extend in opposite directions from the dimethyl­ene bridge. An inter­esting feature of the crystal structure is the short inter­molecular Br⋯F inter­actions [3.2347 (16) Å, which is shorter than the sum of the van der Waals radii of these atoms]. These inter­actions link neighbouring mol­ecules along the c axis. The crystal structure is further stabilized by inter­molecular C—H⋯N hydrogen bonds.

Related literature

For bond-length data, see: Allen et al. (1987 ▶). For halogen–halogen inter­actions, see: Ramasubbu et al. (1986 ▶); Brammer et al. (2003 ▶). For related structures, see, for example: Fun & Kia (2008a ▶,b ▶,c ▶): Fun et al. (2008 ▶). For Schiff base complexes and their applications, see, for example: Pal et al. (2005 ▶); Calligaris & Randaccio, (1987 ▶); Hou et al. (2001 ▶); Ren et al. (2002 ▶).

Experimental

Crystal data

• C₁₆H₁₂Br₂F₂N₂

• M _r = 430.10

• Monoclinic,

• a = 4.1981 (1) Å

• b = 14.6190 (3) Å

• c = 12.8861 (3) Å

• β = 104.751 (2)°

• V = 764.78 (3) ų

• Z = 2

• Mo Kα radiation

• μ = 5.32 mm⁻¹

• T = 100.0 (1) K

• 0.51 × 0.07 × 0.05 mm

Data collection

• Bruker SMART APEXII CCD area-detector diffractometer

• Absorption correction: multi-scan (SADABS; Bruker, 2005 ▶) T _min = 0.172, T _max = 0.769

• 19361 measured reflections

• 2631 independent reflections

• 1907 reflections with I > 2σ(I)

• R _int = 0.050

Refinement

• R[F ² > 2σ(F ²)] = 0.040

• wR(F ²) = 0.100

• S = 1.05

• 2631 reflections

• 100 parameters

• H-atom parameters constrained

• Δρ_max = 1.40 e Å⁻³

• Δρ_min = −0.85 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: APEX2; data reduction: SAINT (Bruker, 2005 ▶); program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2003 ▶).

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C2—H2A⋯N1i	0.93	2.53	3.386 (3)	154

Symmetry code: (i) .

supplementary crystallographic information

Comment

Schiff bases are one of most prevalent mixed-donor ligands in the field of coordination chemistry. There has been growing interest in Schiff base ligands, mainly because of their wide application in the field of biochemistry, synthesis, and catalysis (Pal et al., 2005; Hou et al., 2001; Ren et al., 2002). Many Schiff base complexes have been structurally characterized, but only a relatively small number of free Schiff bases have been characterized (Calligaris & Randaccio, 1987). As an extension of our work (Fun & Kia 2008a,b,c; Fun et al., 2008) on the structural characterization of Schiff base ligands, and the halogen-halogen interactions in the halogen-subtituated Schiff bases, the title compound (I), is reported here.

The molecule of the title compound, (I), (Fig. 1), lies across a crystallographic inversion centre and adopts an E configuration with respect to the azomethine C═N bond. The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable with the related structures (Fun & Kia 2008a,b,c; Fun et al., 2008). The two planar units are parallel but extend in opposite directions from the dimethylene bridge. The interesting feature of the crystal structure is the short intermolecular Br···F interactions [symmetry code: 1 - x, -1/2 + y, 1/2 - z] with the distance of 3.2347 (16) Å, which is shorter than the sum of the van der Waals radii of these atoms. The directionality of these interactions, C—X···X—C (X = halogens), has been attributed to anisotropic van der Waals radii for terminally bound halogens or ascribed to donor-acceptor interactions involving a lone pair donor orbital on one halogen and a C—Xσ^* acceptor orbital on the other (Ramasubbu et al., 1986; Brammer et al., 2003). These interactions link neighbouring molecules along the c-axis (Fig. 2). The crystal structure is further stabilized by intermolecular C—H···N hydrogen bonds (Table 1).

Experimental

The synthetic method has been described earlier (Fun & Kia 2008a). Single crystals suitable for X-ray diffraction were obtained by evaporation of an ethanol solution at room temperature.

Refinement

All of the hydrogen atoms were positioned geometrically with C—H = 0.93 or 0.97 Å and refined in riding model with U_iso (H) = 1.2 U_eq (C). The highest peak is located 1.73 Å from Br1 and the deepest hole is located 0.7 Å from Br1.

Figures

Fig. 1.

The molecular structure of (I) with atom labels and 50% probability ellipsoids for non-H atoms [symmetry code for A: -x, -y, -z.

Fig. 2.

The crystal packing of (I), viewed down the a-axis, shows linking of molecules by Br···F contacts along the c-axis and the stacking of these molecules down the a-axis. Intermolecular interactions are shown as dashed lines.

Crystal data

C16H12Br2F2N2	F(000) = 420
Mr = 430.10	Dx = 1.868 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5643 reflections
a = 4.1981 (1) Å	θ = 3.2–30.0°
b = 14.6190 (3) Å	µ = 5.32 mm−1
c = 12.8861 (3) Å	T = 100 K
β = 104.751 (2)°	Needle, colourless
V = 764.78 (3) Å3	0.51 × 0.07 × 0.05 mm
Z = 2

Data collection

Bruker SMART APEXII CCD area-detector diffractometer	2631 independent reflections
Radiation source: fine-focus sealed tube	1907 reflections with I > 2σ(I)
graphite	Rint = 0.050
φ and ω scans	θmax = 32.0°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2005)	h = −6→6
Tmin = 0.172, Tmax = 0.770	k = −21→21
19361 measured reflections	l = −19→18

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.100	H-atom parameters constrained
S = 1.05	w = 1/[σ2(Fo2) + (0.0539P)2] where P = (Fo2 + 2Fc2)/3
2631 reflections	(Δ/σ)max < 0.001
100 parameters	Δρmax = 1.40 e Å−3
0 restraints	Δρmin = −0.86 e Å−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br1	−0.74079 (7)	−0.51485 (2)	0.18481 (2)	0.02329 (11)
F1	−0.0347 (4)	−0.22639 (11)	0.31348 (12)	0.0267 (4)
N1	−0.0960 (6)	−0.12204 (15)	0.01873 (19)	0.0192 (5)
C1	−0.2112 (7)	−0.27577 (19)	0.2280 (2)	0.0199 (5)
C2	−0.3675 (7)	−0.35336 (19)	0.2493 (2)	0.0206 (6)
H2A	−0.3576	−0.3716	0.3192	0.025*
C3	−0.5404 (7)	−0.40314 (18)	0.1619 (2)	0.0181 (5)
C4	−0.5632 (7)	−0.37558 (19)	0.0569 (2)	0.0215 (6)
H4A	−0.6819	−0.4099	−0.0009	0.026*
C5	−0.4047 (7)	−0.29567 (19)	0.0405 (2)	0.0208 (6)
H5A	−0.4212	−0.2761	−0.0293	0.025*
C6	−0.2210 (6)	−0.24370 (18)	0.1260 (2)	0.0174 (5)
C7	−0.0381 (6)	−0.16150 (18)	0.1090 (2)	0.0182 (5)
H7A	0.1239	−0.1380	0.1659	0.022*
C8	0.1076 (7)	−0.04254 (19)	0.0114 (2)	0.0208 (5)
H8A	0.2171	−0.0516	−0.0456	0.025*
H8B	0.2750	−0.0349	0.0783	0.025*

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Br1	0.02442 (16)	0.01848 (15)	0.02622 (17)	−0.00289 (11)	0.00507 (11)	0.00316 (11)
F1	0.0383 (10)	0.0214 (9)	0.0173 (8)	−0.0032 (7)	0.0014 (7)	−0.0029 (6)
N1	0.0213 (11)	0.0165 (11)	0.0209 (11)	−0.0001 (9)	0.0072 (9)	0.0004 (9)
C1	0.0220 (13)	0.0195 (14)	0.0163 (12)	0.0024 (10)	0.0015 (10)	−0.0035 (10)
C2	0.0261 (14)	0.0187 (13)	0.0168 (13)	0.0035 (10)	0.0051 (11)	0.0018 (10)
C3	0.0191 (12)	0.0153 (12)	0.0209 (13)	−0.0006 (9)	0.0066 (10)	0.0012 (10)
C4	0.0221 (13)	0.0231 (14)	0.0187 (13)	−0.0001 (11)	0.0042 (11)	−0.0006 (11)
C5	0.0231 (13)	0.0197 (13)	0.0185 (13)	0.0003 (10)	0.0034 (11)	0.0022 (10)
C6	0.0192 (13)	0.0142 (12)	0.0196 (13)	0.0031 (9)	0.0064 (10)	0.0015 (10)
C7	0.0182 (12)	0.0151 (12)	0.0210 (13)	0.0016 (9)	0.0042 (10)	−0.0022 (10)
C8	0.0178 (12)	0.0194 (12)	0.0251 (14)	−0.0027 (10)	0.0055 (10)	−0.0026 (11)

Geometric parameters (Å, °)

Br1—C3	1.895 (3)	C4—C5	1.387 (4)
F1—C1	1.366 (3)	C4—H4A	0.9300
N1—C7	1.265 (3)	C5—C6	1.398 (4)
N1—C8	1.460 (4)	C5—H5A	0.9300
C1—C2	1.373 (4)	C6—C7	1.472 (4)
C1—C6	1.387 (4)	C7—H7A	0.9300
C2—C3	1.382 (4)	C8—C8i	1.521 (6)
C2—H2A	0.9300	C8—H8A	0.9700
C3—C4	1.391 (4)	C8—H8B	0.9700
C7—N1—C8	116.3 (2)	C4—C5—H5A	119.1
F1—C1—C2	117.7 (2)	C6—C5—H5A	119.1
F1—C1—C6	117.7 (2)	C1—C6—C5	116.2 (2)
C2—C1—C6	124.6 (3)	C1—C6—C7	121.8 (2)
C1—C2—C3	116.8 (3)	C5—C6—C7	122.0 (2)
C1—C2—H2A	121.6	N1—C7—C6	121.6 (2)
C3—C2—H2A	121.6	N1—C7—H7A	119.2
C2—C3—C4	122.2 (2)	C6—C7—H7A	119.2
C2—C3—Br1	119.2 (2)	N1—C8—C8i	109.6 (3)
C4—C3—Br1	118.6 (2)	N1—C8—H8A	109.8
C5—C4—C3	118.4 (3)	C8i—C8—H8A	109.8
C5—C4—H4A	120.8	N1—C8—H8B	109.8
C3—C4—H4A	120.8	C8i—C8—H8B	109.8
C4—C5—C6	121.9 (3)	H8A—C8—H8B	108.2
F1—C1—C2—C3	−179.0 (2)	F1—C1—C6—C7	2.4 (4)
C6—C1—C2—C3	1.3 (4)	C2—C1—C6—C7	−177.9 (3)
C1—C2—C3—C4	−1.5 (4)	C4—C5—C6—C1	−1.1 (4)
C1—C2—C3—Br1	176.3 (2)	C4—C5—C6—C7	176.7 (3)
C2—C3—C4—C5	0.4 (4)	C8—N1—C7—C6	−178.5 (2)
Br1—C3—C4—C5	−177.4 (2)	C1—C6—C7—N1	−165.9 (3)
C3—C4—C5—C6	1.0 (4)	C5—C6—C7—N1	16.4 (4)
F1—C1—C6—C5	−179.8 (2)	C7—N1—C8—C8i	−115.8 (3)
C2—C1—C6—C5	−0.1 (4)

Symmetry codes: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, °)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···N1ii	0.93	2.53	3.386 (3)	154.

Symmetry codes: (ii) x, −y−1/2, z+1/2.